Optic and proton dual-control of the fluorescence of Rhodamine based on photochromic diarylethene: mimicking the performance of an integrated logic gate

Article abstract of DOI:10.1016/j.tetlet.2009.01.093

A proton and optic dual-responsive fluorescence switch dyad which contains Rhodamine and photochromic diarylethene has been designed and an integrated logic circuit at the molecular level has been proposed.

Full text of DOI:10.1016/j.tetlet.2009.01.093

Tetrahedron Letters 50 (2009) 1588–1592
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Optic and proton dual-control of the fluorescence of Rhodamine based
on photochromic diarylethene: mimicking the performance
of an integrated logic gate
Haiyan Zheng, Weidong Zhou, Mingjian Yuan, Xiaodong Yin, Zicheng Zuo, Canbin Ouyang, Huibiao Liu,
*
Yuliang Li , Daoben Zhu
Beijing National Laboratory for Molecular Science (BNLMS), CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences and Graduate School of
Chinese Academy of Sciences, Beijing 100190, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A proton and optic dual-responsive fluorescence switch dyad which contains Rhodamine and photochro-
mic diarylethene has been designed and an integrated logic circuit at the molecular level has been
proposed.
Received 6 November 2008
Revised 14 January 2009
Accepted 16 January 2009
Available online 23 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Regulation of molecular fluorescence through external stimuli
such as light, chemical, and electronic signals attracts much atten-
tion due to potential application in sensors,1–3 switches,4–6 high
density optical data storage,7 and logic gates.8–11 In particular,
the regulation of fluorescence properties based on the photochro-
mic compounds has been studied extensively. The energy transfer
(ET) from the fluorescent dye to one of the isomers of the photo-
chromic switch is a powerful tool to modulate the fluorescence.
A lot of examples have been reported by Irie,12–14 Branda,15
Tian,16,17 and Feringa.18 Furthermore, in order to construct multi-
functional logic system, development of smart system in which
the fluorescence can be tuned by several signals is much more
important.19,20
turn to the open-ring forms when they are interacted with protons
or metal ions accompanied with emission in visible region. Thus it
is possible to modulate the fluorescence intensity of the Rhoda-
mine by the chemical inputs.23–25 In this Letter, we have designed
and synthesized a dyad with covalently bonded Rhodamine and
diarylethene. Rhodamnie existed in ring-open form shows emis-
sion in the range of 540–700 nm which has a certain overlap with
the absorption of diarylethene in closed form whereas there is not
in open form. Thus, the energy transfer process from Rhodamine
unit (ET donor) to diarylethene unit (ET acceptor) will be regulated
by the light.26–28 Moreover, the emission intensity of the Rhoda-
mine unit will be also modulated by the proton. Based on these re-
sults, an integrated digital circuit is proposed.
Among various photochromic compounds, diarylethene has re-
ceived much attention owing to the thermally irreversibility, excel-
lent fatigue resistance, highly efficient photo-isomerizations and
rapid response.21 Upon irradiation by ultraviolet light, the colorless
opened-form isomers can transfer to closed-form accompanied
with the appearance of the new absorption. The absorption spectra
of the closed-form depend on the substitutions of thiophene
rings.21 Thus, it is possible to regulate the emission intensity of
the fluorophore through the optical stimuli when its emission
spectrum overlaps the absorption spectrum of the diarylethene
in closed-form, which functions as an ET acceptor.
Rencently, Rhodamine-based dyes have received increasing
interest because they have several advantages: large molar extinc-
tion coefficients, high fluorescence quantum yields, and visible
wavelength excitation.22 In addition, the Rhodamine chromor-
phore has two distinct conformations: colorless spirocyclic form
and red ring-open form. Commonly, the colorless spirocyclic forms
The synthetic route of the dyad is illustrated in Scheme 1. Com-
pound 229 and Rhodamine derivative 530 were obtained according
to described methods. Compound 3 was prepared by coupling p-
bromoanisole to the bis(boronic ester) which obtained from com-
pound 2 through Suzuki reaction.31 Treatment of compound 3 with
an excess amount of boron tribromide afforded 4 quantitatively,
which subsequently reacted with compound 5 in DMF at 60 °C in
the presence of anhydrous K2CO3 to give dyad 1 in good yield.
The photochromic behavior of the dyad 1 was studied by UV–
vis absorption spectra and 1H NMR. As shown in Figure 1, dyad 1
shows strong absorption in the UV region indicating that the diary-
lethene unit is in the opened form.21 After irradiating the solution
of dyad 1 in acetonitrile at 312 nm for 1.5 min, the colorless solu-
tion turned purple and new absorption bands centered at 360 nm
and 518 nm were observed, indicating the formation of the closed
form of the diarylethene moiety.21 The process of photocyclization
reaction was also monitored by 1H NMR. After 90 min of irradia-
tion, the photostationary state was reached and about 71% of the
opened form (1O) converted to the closed form (1C). In the 1H
NMR spectrum of dyad 1, a new peak appeared at upfield
* Corresponding author. Tel.: +86 10 62588934; fax: +86 10 82616576.
E-mail addresses: ylli@iccas.ac.cn (Y. Li), steven_zhou1981@hotmail.com (Y. Li).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.01.093

H. Zheng et al. / Tetrahedron Letters 50 (2009) 1588–1592
1589
Scheme 1. Synthetic route for dyad 1.
Figure 2. Emission spectra of dyad 1 (5 Â 10À6 M, CH3CN, 25 °C) in the presence of
10 equiv of TFA (5 Â 10À3 M, CH3CN), and 10 equiv of TFA + 30 equiv of TEA
(5 Â 10À3 M, CH3CN) excited at 530 nm.
Figure 1. Absorption spectra of dyad 1 (5 Â 10À6 M, CH3CN, 25 °C) before (solid
line) and after (dashed line) irradiation with light of 312 nm for 1.5 min. Inset: The
absorption at 518 nm during alternate irradiation at 312 nm and visible light
(k > 400 nm) for 1.5 min.
gion almost completely disappeared which indicates the photo-
chromic process is reversible. The inset of Figure 1 shows the
change of absorption at 518 nm during alternate irradiation by
ultraviolet light (k = 312 nm) and visible light (k > 400 nm). It indi-
cates the dyad 1 can undergo several ring opening-closing cycles
with slight fatigue in the absorption spectrum.
(1.85 ppm) assigned to the methyl group (Ha) of 1C32 and the thi-
ophene C–H (Hb) signal shift to the upfield (7.09 ppm for 1O,
6.60 ppm for 1C) which indicates the lose of the aromatic character
of the thienyl moiety33 (see Supplementary data). Upon irradiation
of visible light (k > 400 nm), the absorption band in the visible re-

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H. Zheng et al. / Tetrahedron Letters 50 (2009) 1588–1592
Scheme 2. The dual-mode fluorescence switching principle of dyad 1 with four external stimuli: UV light (k = 312 nm), visible light (k > 400 nm), TFA and TEA.
As expected, the emission intensity of the Rhodamine unit in
dyad 1 can be tuned by chemical signals. Figure 2 shows the emis-
sion spectra of dyad 1 with excitation at 530 nm in CH3CN upon
addition of trifluroacetic acid (TFA) and triethylamine (TEA). Ini-
tially, the solution of dyad 1 in CH3CN was nonfluorescent by exci-
tation at 530 nm. Upon addition of 10 equiv of TFA, the color of the
solution of dyad 1 became purple progressively and a broad emis-
sion band in the range of 540–680 nm with the maximum at
581 nm appeared due to the formation of the strongly fluorescent
ring-opened Rhodamine. With addition of excess TEA to the solu-
tion, the Rhodamine unit switched to spirocyclic form and the
intensity of the fluorescence at 581 nm decreased to 18% of that
of the solution in acidic condition after reaching to the stationary
state.
The fluorescence intensity of the dyad 1 can also be regulated
reversibly by the alternation of ultraviolet and visible light stimuli.
The emission spectrum of dyad 1 in CH3CN under acidic condition
recorded the transformation. After acidification, it appeared a
broad emission band in the range of 540–680 nm with the maxi-
mum around 581 nm ascribed to the formation of the ring-opened
amide form of Rhodamine (Fig. 3 solid line). The luminescence of
dyad 1 in acidic condition greatly depends on the state of the diay-
lethene photoswitch. In the open form, the Rhodamine in acidic
condition displayed strong fluorescence at 581 nm when excited
at 530 nm. When the photocyclization reaction was carried out
by irradiating the dyad 1 with ultraviolet light, the emission inten-
sity around 581 nm decreased to 38% of that of initial state (Fig. 3
Figure 3. Emission spectra of dyad 1 (5 Â 10À6 M, CH3CN, 25 °C) in the presence of
10 equiv of TFA (5 Â 10À3 M, CH3CN) (solid line), irradiation with ultraviolet light
(k = 312 nm) for 1.5 min (dashed line) and irradiation with visible light (k > 400 nm)
for 1.5 min (dotted line). Inset: Reversible modulation of the emission intensity of
dyad 1 (5 Â 10À6 M, CH3CN, 25 °C) in the presence of 10 equiv of TFA (5 Â 10À3 M,
CH3CN) with the ultraviolet (I1) and visible light (I2), the excitation wavelength is
530 nm.

H. Zheng et al. / Tetrahedron Letters 50 (2009) 1588–1592
1591
Thus, the dyad 1 can read a string of three inputs and write a
unique fluorescence output. For example, when the input string
is 100, corresponding to the I1, I2 and I3 are on, off, off, respec-
tively. Under these conditions, the dyad 1 is in state 3 and the fluo-
rescence of the Rhodamine unit is quenched. Hence, the output
signal is off. If the I1, I2 and I3 are all off, the input string is 000.
Under these conditions, the dyad 1 is in state 2 and the relative
intensity of the fluorescence is 100%. Thus, the output signal O1
is on and the output digit is 1. All the possible strings of the three
inputs are listed in Table 1 and the combinational logic circuits
equivalent to the truth table is illustrated in Figure 4.
In conclusion, a novel dyad 1 with proton-sensitive and photo-
chromic components has been synthesized and characterized. The
emission intensity of the dyad 1 can be regulated by chemical and
optical stimuli. Based on the fact, an integrated digital circuit with
three external input signals and one fluorescence output signal
was constructed and the information transmission at the single
molecular level was realized.
Figure 4. The combinational logic circuits equivalent to the truth table gave in
Table 1.
Table 1
Truth table for all possible strings of three binary-input data and the corresponding
output digit (combinational logic circuits corresponding to the truth table is given in
Fig. 4)
Acknowledgments
Input
Outputa
This work was supported by the National Nature Science Foun-
dation of China (20831160507 and 20721061) and the National Ba-
sic Research 973 Program of China.
I1 (UV)
I2 (vis)
I3 (TEA)
kem = 581 (nm)
0
1
0
0
1
1
0
1
0
0
1
0
1
0
1
1
0
0
0
1
0
1
1
1
1
0
1
0
1
0
0
0
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.01.093.
a
At 581 nm, the emission intensity below 40% of the original value is defined as
0, otherwise defined as 1.
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